1. Field of the Invention
The present invention relates to an accumulator which is used as a pressure accumulating apparatus or a pulse pressure damping apparatus. The accumulator in accordance with the present invention is used, for example, for a hydraulic piping or the like in a vehicle such as a motor vehicle or the like.
2. Description of the Conventional Art
Conventionally, as shown in FIG. 11, there is known an accumulator 51 in which an internal space of an accumulator housing 52 provided with a gas sealing port 54 as well as being provided with an oil port 53 connected to a pressure piping (not shown) is comparted into a gas chamber 57 in which gas is charged, and a liquid chamber 58 which communicates with the oil port 53 by a bellows 55 with a bellows cap 56, and the bellows cap 56 moves and the bellows 55 expands and contracts to make gas pressure and liquid pressure balance, thereby the accumulator being actuated so as to accumulate pressure or actuated so as to damp pulse pressure (refer to Japanese Unexamined Patent Publication No. 2003-172301).
Further, the accumulator 51 is provided with a safety mechanism (a safety mechanism for a pressure drop time) 59 preventing the bellows 55 from being broken on the basis of unbalance between the gas pressure and the liquid pressure, at a time when pressure of the pressure piping is lowered, and pressure of the liquid chamber 58 is lowered. In other words, if the pressure of the pressure piping is extremely lowered by stopping of an operation of an equipment or otherwise, the liquid (oil) is discharged little by little from the oil port 53, the bellows 55 contracts little by little by the charged gas pressure in accordance with this, and a seal 60 provided on a lower surface of the bellows cap 56 comes into contact with a stay 61 so as to come to a so-called zero down state. The stay 61 is a single metal formed product in which a liquid passage 61c is provided in an end face portion 61b on the end of a tubular portion 61a. Further, in this zero down state, since a part of liquid is confined in the liquid chamber 58 by the seal 60, and the pressure of the confined liquid and the gas pressure of the gas chamber 57 balance, it is possible to inhibit the bellows 55 from being broken on the basis of application of excessive stress to the bellows 55.
Further, the accumulator 51 is provided with a safety mechanism (a safety mechanism for an emergency time) 62 preventing the liquid within the liquid chamber 58 and the gas within the gas chamber 57 from rapidly expanding so as to make the accumulator 51 explode, at an emergency time such as fire occurrence. In other words, if the liquid within the liquid chamber 58 and the gas within the gas chamber 57 are rapidly expanded due to the occurrence of a fire or the like, a rupture plate 61d provided circumferentially locally in a peripheral surface of the stay 61 is ruptured by this high pressure so that the high pressure is released therefrom, thereby inhibiting an internal portion of the accumulator 51 from becoming extremely high pressure so as to explode.
However, in the conventional art mentioned above, since the safety mechanism 62 for the emergency time is constructed by the rupture plate 61d provided circumferentially locally in the peripheral surface of the stay 61 as mentioned above, there is such a disadvantage that rupture pressure is high (such great pressure as to rupture the metal plate is necessary) and accordingly the safety mechanism 62 for the emergency time is not actuated until the pressure becomes extremely high pressure. Further, it can be thought to provide a fusible plug or a valve in place of the rupture plate 61d. However, the fusible plug is not actuated until the plug itself becomes high temperature, and the valve has such a risk that the valve may be erroneously opened (erroneously activated) at the other times than the emergency time on the basis of its mechanical structure.